Heat exchanger



Augi4, 1959 w. o. WEBBER ET AL 2,897,338 HEAT EXCHANGER Filed July 29,1957 FIG. I.

ALKLATION I Asmsmofl OLEFINS 2 1 AND ISOPARAFFINS '51 v I AEMULSION PUMPl3 1% I4 27 was MAKE UP ACID 22 37 u 11 1W i 5 37a -38 FIG. 2.

FIG. 3.

t INVENTORS. W|H|am O. Webber, J Delmos A. Smith,

United States Patent Chi ice HEAT EXCHANGER William 0. Webber and DelmasA. Smith, Baytown,

Tex., assignors, by mesne assignments, to Esso Research and EngineeringCompany, Elizabeth, N.J., a corporation of Delaware Application July 29,1957, Serial No. 674,807

3 Claims. (Cl. 138-38) The present invention is directed to a heatexchanger. More particularly, the invention is concerned with a heatexchanger having improved heat transfer characteristics. In its morespecific aspects, the invention is directed to a heat exchanger of theshell and tube type provided with means in the heat exchanger tubes forimproving heat transfer characteristics.

The present invention may be briefly described as a heat exchanger ofthe shell and tube type having improved heat transfer characteristicswhich comprises an elongated supporting member longitudinally arrangedin each of the tubes of the heat exchanger and a plurality ofhorizontally spaced apart means carried on and supported by thesupporting member for creating turbulent flow in the tubes, thesupporting member being arranged against the walls of the tubes and theturbulent flow creating means being preferably substantially co-axialwith the tubes.

The turbulent flow creating means employed in the present inventionsuitably comprises a plurality of discs arranged on and supported by anelongated supporting member arranged in the tubes of the heat exchanger,the supporting member being arranged along the Walls of the tubes whilethe discs are arranged to project into the path of flow through thetubes to cause mixing or turbulence. The supporting member is preferably'a crimped metal wire having metallic discs welded to the wire on theinner side of the crimps. The wire may carry discs hon'zontally spacedapart a distance in the range from about 0.25 to about feet. Discsspaced apart about 1 foot give very desirable results.

The discs are preferably concentric with the tubes but may be arrangedeccentric with respect to the axis of the tubes.

The turbulent flow creating means or discs may be suitably sized toprovide an area of flow through the tubes no greater than about 75% ofthe diameter of the tubes to create the turbulence. Desirable resultsare ob tained with an area of flow of about 64% of the tube diameter.

The invention is directed also to heat exchangers Which employ finnedtubes which serve to increase the efficiency of the heat exchanger.

The present invention is particularly adaptable for use in reactionsinvolving mixing of dissimilar fluids. For example, it is suitable inalkylation reactions where an emulsion of acid and hydrocarbon reactantsis contacted.

In using the present invention in alkylation reactions, the emulsion iscirculated through a heat exchanger employing the present inventionwhich serves to improve the heat transfer rate and improve efficiency ofthe operation.

The invention will be further illustrated by reference to the drawing inwhich:

Fig. l is a schematic flow diagram showing the present invention used inan alkylation reaction;

Fig. 2 is a cross-sectional view of a heat exchanger 2,897,838 PatentedAug. 4, 1959 tube provided with a supporting member and discs inaccordance with the present invention; 7

Fig. 3 is a partial view of the supporting member of the presentinvention;

Fig. 4 is a view showing a disc attached to the supporting member; and

Fig. 5 is a view taken along the lines 5-5 of Fig. 4;

Referring now to the drawing, and particularly to Fig; l, numeral 11designates an alkylation reactor into which a mixture of olefins andisoparafl'ins is introduced by way of line 12. The olefins may suitablycomprise butylenes or pentylenes, while the isoparaffins may suitablycomprise isobutane, isopentane, and the like. While these particularolefins and isoparafiins in an alkylation reaction are given by way ofillustration and not by way of limitation, the invention is applicableto many types of reactions involving heat transfer. The mixture ofolefins and isoparafiins, with the olefins and isoparalfins employed ina ratio in the range from about 1:2 to about 1:10, is contacted in thealkylation reactor 11 with an emulsion of the hydrocarbon reactants anda sulfuric acid catalyst introduced into the system by way of line 13,controlled by valve 14. The sulfuric acid may have a strength in therange from about to about percent H 80 The emulsion is circulatedthrough the alkylation reactor 11 by way of line 13 to which theemulsion is supplied by way of line 15 from a source which Will bedescribed further, and the admixture is suitably contacted in reactionzone 11 to cause the reaction to proceed to form an alkylated product.The product is withdrawn from reaction zone 11 by way of line 16 and discharged into a product accumulator 17 which is of sufficient capacity toallow a separation to be made between the acid and hydrocarboncomponents of the emulsion, The separated hydrocarbon product iswithdrawn by way of line 18 for separation of high octane numberconstituents therefrom, while the acid phase of the emulsion iswithdrawn by way of line 19 and may suitably be reintroduced into thesystem as may be desired.

Since the reaction proceeds best at a temperature in the range fromabout 35 to about 55 F., it is desirable to maintain a temperaturewithin this range at about 40 F. To this end, a portion of the emulsionis withdrawn from the alkylation reactor 11 by line 20 and introducedinto a heat exchanger 21 of the shell and tubetype, wherein the emulsionis circulated through the bank of tubes 22 and, with heat transfer froma body 23 of evaporating light hydrocarbon, is suitably .cooled onpassage through the bank of tubes 22. The

cooled emulsion is then discharged from the bank of tubes 22 by way ofline 24 into an emulsion accumulator 25 for recirculation by way of line26 and line 15 back into the alkylation reactor 11. It is to be notedthat line 15 is provided with an emulsion pump 27, and line 26 isprovided With a valve 28 for discharge of acid to maintain the strengthof the acid in the system by introducing a like amount of fresh acid byway of line 13, controlled by valve 14.

The temperature control in heat exchanger 23 is maintained byevaporating the light hydrocarbon, such as butane, forming the body 23.To this end, vapors of the light hydrocarbon are withdrawn fromthe vaporspace 29 by way of line 30, compressed in compressor 31, then introducedby line 32 into cooler 33, from whence the cooled and compressed vaporsare introduced by line 34 into a condensate drum 35, wherein thecondensate accumulates for return by line 36 to the body 23.

The tubes 22 of heat exchanger 21 have arranged in each of the tubes 22an elongated supporting member 37, which is shown more clearly in Fig.2. The elongated supporting member 37 is formed to provide crimps 37a towhich the discs 38 are attached by spot Welding,

It is to be noted that the elongated supporting member 37, whichsuitably may be a wire of suflicient strength, is arranged along thewall of tubes 22 while the crimps and the discs attached thereto projectacross the tubes such that the discs are preferably co-axial with theaxis of the tubes 22.

Referring to Figs. 3, 4, and 5, the supporting member 37 and the discs38 are shown more clearly. Referring to Fig. 3, the supporting member 37is provided with crimps 37a throughout its length, with the crimpshaving an overall height of about 0.77. The supporting member 37 maysuitably be constructed of 12 gauge type 304 wire.

Referring to Figs. 4 and 5, it will be seen that the discs 38 are weldedby spot Weld 39 to the inner surface of the crimps 37a.

As an example of a heat exchanger having tubes of about 16.5 in length,a wire supporting member will be provided with about 15 crimps about 12"apart, to which the discs will be welded. These discs may have anoutside diameter of about 0.4" and be about A thick.

The discs may suitably be constnucted of metal, but

may be constructed of other material which is resistant to the fluidswith which it comes into contact. For example, the discs may beconstructed of a plastic, such as Teflon, which ispolytetrafluoroethylene. Other suitable construction materials for thediscs may include Hastelloy B and other alloys of a similar nature.

The present invention is quite advantageous and useful in that itimproves heat transfer, and in an alkylation operation such asdescribed, the improved heat transfer allows the use of a lower over-alltemperature difference. For example, when butane is evaporating outsidethe tubes of the heat exchanger 21, inside of which flows an emulsion ofacid and hydrocarbon reactants, the butane on the outside of the tubesmay evaporate at a higher temperature than heretofore. temperature meansthat evaporation may be conducted at a higher pressure and thus therefrigerant vapors are sent to the compressor at a higher suctionpressure, which allows the compressor to work through a lowercompression ratio, defined as discharge pressure divided by the suctionpressure, which requires less horsepower. For example, a horsepowersavings of about 500 may be achieved employing the present invention ina heat exchanger system in an alkylation reaction.

The present invention has been used successfully over a long period oftime in a commercial alkylation plant in which olefins are alkylatedwith isoparaflins using sulfuric acid as a catalyst. By employing thepresent invention, heat transfer rate was increased approximately to 50percent over that obtainable prior to installation of the presentinvention.

Operation at an increased The placement of a supporting member adjacentthe wall of the heat exchanger tubes does not increase the pressure dropsubstantially. In other words, the effect of the supporting member onpressure drop is negligible, and the pressure drop experienced byemploying turbulent fiow creating means is accounted for substantiallyby the installation of the metal discs on the metallic sup portingmember.

The size of the metallic discs employed on the supporting member isselected such that they are substantially equal in diameter to providean area of flow through the tubes no greater than about percent of thediameter of the tubes. In other words, the passage around the metallicdiscs should be below about 75 percent of the pipe diameter. In acommercial installation very satisfactory results were obtained withabout 64 percent area open for flow.

The nature and object of the present invention having been completelydescribed and illustrated, what we wish to claim as new and useful andsecure by Letters Patent 1. A heat exchanger tube adapted for use in aheat exchanger of the shell and tube type, said tube having improvedheat transfer characteristics and having an elongated crimped wirelongitudinally arranged therein, and a plurality of horizontally spacedapart discs secured to the wire on the inner side of the crimps, saidwire being arranged against the wall of the tube and said disc beingsubstantially coaxial with the tube.

2. A heat exchanger tube in accordance with claim 1 in which the discsare sized to provide an area of flow no greater than about 75% of thediameter of the tubes.

3. A heat exchanger tube adapted for use in a heat exchanger of theshell and tube type, said tube having improved heat transfercharacteristics and having an elongated crimped wire longitudinallyarranged therein,

and a plurality of horizontally spaced apart discs secured to the wireon the inner side of the crimps, said discs being substantially equal indiameter, said wire being arranged against the wall of the tube, andsaid discs being substantially coaxial with the tube.

References Cited in the file of this patent UNITED STATES PATENTS

